The subject matter disclosed herein relates to a helicopter engine inlet and, more particularly, to a helicopter engine inlet with variable geometry.
A problem with high speed rotorcraft is the need to balance external aerodynamic performance with engine inlet performance. Larger inlet capture areas are required for higher engine performance at lower speeds and especially hover conditions to permit a greater amount of air to flow into the engine than would be possible at low speeds or hover conditions with relatively small inlets. These larger inlet capture areas, however, do not provide appreciable engine performance benefit at higher speeds and in many cases act to the detriment of the overall aerodynamic performance of the aircraft. Moreover, the larger inlet capture areas tend to be oversized in the presence of ramming air at high speeds and thus may result in inlet spillage. Such spillage, when coupled with the larger exposed surface facing into the freestream flow, may result in higher drag.
Prior solutions for sizing rotorcraft inlets have required that a fixed inlet size be chosen. The fixed inlet size necessitates a performance compromise in either engine performance at lower speeds and hover, greater aircraft drag at higher speeds or a combination of the two if a design is chosen in the middle range of inlet sizes.
Other prior solutions have given rise to variable geometry inlets but these have generally been used only for supersonic fixed wing aircraft and, most often to mitigate supersonic shock.